In downflow reactors, such as downflow reactors, a layer of filtering material is often placed on top of the first catalyst bed to catch particles such as fines and scales. Typically, this layer may be 6 to 36 inches thick and reduces the space available for the catalyst to take up. In addition, the filtering material has to be removed and replaced within an operating cycle when solids accumulates within the layer of filtering material or between the filtering material and catalyst bed causing high pressure drop.